He joined East Malling (now NIAB EMR) in 2011 as a research leader developing into his role as the head of the genetics, genomics and breeding department in 2016. In his new role he leads one of four business units in NIAB- Cambridge Crop Research, which encompasses the following departments:

Genetics and Breeding
Pathology and Entomology- led by Dr Jane Thomas
Agricultural Crop Characterisation - led jointly by Dr Margaret Wallace and Mr Stephen Flack
Plant Biotechnology- led by Dr Emma Wallington
Computational Biology - led by Dr Ji Zhou
Plant Breeding - led by Dr Phil Howell
His own research focuses on understanding the genetic basis of complex traits, often using interactions between plants and microbes as a study system. While at East Malling he developed research in horticultural crops such as strawberry, apple and cherry.

Dr Harrison is a member of the BBSRC Agri-food Strategic Advisory Panel, the KTN Plant Science advisory board, and the BBSRC pool of experts.